The present invention relates to a method for controlling intake flow for an internal combustion engine, and to a control system which practices said method; and more specifically relates to an intake control method and system for an internal combustion engine which is provided with an intake port construction including both direct and helical intake passages, whereby the relative amounts of intake flow which pass through said direct intake passage and said helical intake passage can be varied.
There are some types of variable swirl intake port construction for an internal combustion engine, which have been developed by colleagues of the present inventors in the works of the assignee of the present application previously to the development of the present invention, for the inventive concepts of which Japanese Patent Applications Ser. Nos. 56-51149 and 56-120634 were filed previously to the filing of Japanese Patent Application Nos. 56-105017, 56-105018 and 56-105019 relating to the present invention of which priority is being claimed in the present application, and for said inventive concepts of which it is known to the present inventors that U.S. patent application Ser. Nos. 341,911 and 404,145 have been filed claiming the priority of the above identified Japanese patent applications, which incorporate two intake passages formed as leading to the opening past the intake poppet valve into the combustion chamber of the engine, one of said passages leading substantially straight to said opening, and the other leading in a curved or helical path to said opening. The first or the straight one of said intake passages is controlled by an intake control valve mounted at an intermediate position therealong, so that its effective flow resistance is variable; and thus the relative amounts of intake flow which pass through said direct intake passage and said helical intake passage can be varied. In other words, when said intake control valve is closed to the maximum extent (i.e., in general, is fully closed), then a maximum proportion of the intake flow (of air or of air/fuel mixture, according to the particular application) which is sucked in by the combustion chamber through the intake port construction is sucked in through the helical intake passage and a minimum proportion of said intake flow is sucked in through the straight intake passage, so that as a whole a maximum amount of swirling is imparted to the intake gas sucked into the combustion chamber. On the other hand, when said intake control valve is closed to the minimum extent (i.e., in general, is fully opened), then a minimum proportion of the intake flow sucked in by the combustion chamber through the intake port construction is sucked in through the helical intake passage and a maximum proportion of said intake flow is sucked in through the straight intake passage, so that as a whole a minimum amount of swirling is imparted to the intake gas sucked into the combustion chamber. Such a type of variable swirl intake port construction for an internal combustion engine is shown in FIGS. 1 through 7 of the accompanying drawings, and will be more fully explained in the portion of this specification entitled "DESCRIPTION OF THE PREFERRED EMBODIMENTS".
When the intake flow of an internal combustion engine is imparted with a strong swirling, as in the above described case when the aforesaid intake control valve in the straight intake passage is closed as far as possible so that most or all of the intake flow of the engine passes through the helical intake passage, then the apparent flame propagation speed is increased, and it is possible to operate the engine with a very lean mixture, i.e. with a high air/fuel ratio. Further, strong intake swirling helps with stable idling of the engine, so that, other things being equal, the idling speed can be set very low. On the other hand, the intake volumetric efficiency is reduced, especially during high load engine operation. But in the case when no or very little swirling is provided, as in the above described case when the aforesaid intake control valve in the straight intake passage is opened as far as possible so as to combine the flow through said straight intake passage with the flow through the helical intake passage, then the apparent flame propagation speed is lower and the engine cannot be operated on mixture of such a low air/fuel ratio, and the idling speed cannot be set so low and the idling is not so stable, but on the other hand the intake volumetric efficiency is much higher.
Thus, in the above-identified prior applications, in the engine operational region from low to medium load it was intended to provide high swirling for the gases entering the combustion chamber, by closing said intake control valve so as to eliminate flow through said straight intake passage and so as to concentrate flow in said helical intake passage, while in the engine operational region from medium to high load it was intended to provide low swirling for the gases entering the combustion chamber, by opening said intake control valve so as to promote flow through said straight intake passage while reducing the concentration of flow in said helical intake passage and to increase volumetric efficiency. However, such a simplistic control method would not be effective, for the following reason.
Since when as described above the apparent flame propagation speed increases due to increased swirling the combustion speed and efficiency also increase and the thermal efficiency of the engine also increases, at the same time the temperature of the exhaust gases of the internal combustion engine decreases. Thus, if even when the engine is being warmed up and has not attained is proper operating temperature said intake control valve is kept closed so as to eliminate flow through said straight intake passage and so as to concentrate flow in said helical intake passage in order to promote intake swirling, then hot exhaust gases will not be obtained and warming up of the exhaust system of the engine will be delayed. In the case of an internal combustion engine which is provided with a catalytic converter for the purposes of exhaust gas purification, this means that the catalytic converter also will not be warmed up very quickly as the engine is being warmed up, and, since the effectiveness of a catalytic converter for purifying the exhaust gases of an internal combustion engine is critically dependent upon said catalytic converter being brought to the warmed up condition, this has very bad results from the standpoint of production of harmful pollutants in the exhaust gases of the engine.
However, merely to leave said intake control valve in the open state at all times when the engine is not yet warmed up, so as to promote flow through said straight intake passage and so as to reduce the concentration of flow in said helical intake passage, in order to reduce intake swirling so as to warm up the exhaust gases and thus to warm up such a catalytic converter attached to the exhaust system of the internal combustion engine as quickly as possible, would not be an adequate method of control either, because in this case the drivability during idling operation of the engine, and the stability of idling, which are bad enough in any case when the engine is cold, would be further deteriorated to a very low level, and it would be necessary to set the idling speed of the engine at an unacceptably high level, in order to ensure that the engine would idle reliably at all.